Frequency fine-adjusting apparatus for a piezo-electric oscillator

ABSTRACT

Piezo-electric oscillators are widely used in reference clocks for various apparatus. Prior to use, the oscillation frequency of the piezo-electric oscillators is generally finely adjusted. For this purpose, a frequency fine-adjusting apparatus includes a laser beam generator for emitting a laser beam having a wavelength of 2 μm or less, a target material having a metallic layer, a set of rollers for feeding the target material in the condition in which the metallic layer confronts the main electrode of the piezo-electric oscillator and is spaced a predetermined length from the main electrode, and an optical system for applying the laser beam to the metallic layer. When the laser beam is applied to the metallic layer, part of the metallic layer is vaporized and adheres to the surface of the main electrode, thereby finely adjusting an oscillation frequency of the piezo-electric oscillator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a frequency fine-adjusting apparatusfor a piezo-electric oscillator to be used in reference clocks forvarious apparatus.

2. Description of the Prior Art

A piezo-electric oscillator in which a single crystal of a crystal orthe like is used has an extremely large Q factor which is sufficient toensure a highly stable performance. Therefore, a high-level technique isrequired for the fine adjustments of the oscillation frequency. Althoughvarious oscillation modes exist in piezo-electric oscillators, athickness slip mode is generally used. In this thickness slip mode, theoscillation frequency of the piezo-electric oscillator is inverselyproportional to the thickness of an oscillating reed. It is known thatthe oscillation frequency can be lowered by making use of the massadditional effect with respect to a main electrode. Conventionally, theoscillation frequency has been finely adjusted by the use of the massadditional effect.

FIG. 4 depicts the construction of a crystal oscillator, which is one ofthe piezo-electric oscillators.

Referring to FIG. 4, an oscillating reed 20 is provided with a mainelectrode 21, which is supported on a holder 24 of a lead terminal 23 bya conductive bonding agent 22 so that the main electrode 21 and the leadterminal 23 may be electrically connected to each other. The leadterminal 23 is guided out of a case 26 through hermetic sealing glass25. After the oscillation frequency has been finely adjusted, asecondary electrode 27 is formed on a central portion of the mainelectrode 21.

FIG. 5 depicts the construction of a conventional frequencyfine-adjusting apparatus for a crystal oscillator.

As shown in FIG. 5, an oscillating circuit 32 is initially connected toa crystal oscillator 28, the oscillation frequency of which generallyvaries before the frequency fine-adjustment is carried out. The crystaloscillator 28 is then accommodated in a vacuum container 29. After thevacuum container 29 has been evacuated, the oscillation frequency isread by a counter 33 while silver particles 31 for finely adjusting thefrequency are caused to adhere to the main electrode 21 through a mask30 so that the secondary electrode 27 may be formed on the mainelectrode 21. When a comparator 34 detects that the oscillationfrequency has been lowered to a preset value due to the mass additionaleffect, the vacuum evaporation is suspended by a shutter 35. In thisway, the oscillation frequency is finely adjusted.

The frequency fine-adjusting apparatus employing such a vacuumevaporation method requires a high vacuum of approximately 10⁻⁵ Torr andthe costs of vacuum equipment are excessive. Furthermore, the operationefficiency is relatively low due to the batch processing.

Japanese Patent Laid-open Application No. 59-13412 discloses a method ofraising the frequency by removing the main electrode using a laser.

In this method, the main electrode for imparting an electric field to anoscillating reed is partially removed, and the area to be removedbecomes larger as the frequency is adjusted more accurately. As aresult, the electric field to be imparted to the oscillating reedbecomes weaker and the equivalent resistance is increased. Furthermore,the amount of frequency adjustment which exerts no influence upon theequivalent resistance is relatively narrow in the range of adjustmentand cannot allow the change of frequency after the evaporation.Accordingly, this kind of method is disadvantageous in that thefrequency adjustment cannot be achieved satisfactorily.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been developed to substantiallyeliminate the above discussed disadvantages inherent in the prior artfrequency adjusting apparatus for a piezo-electric oscillator, and hasas its essential object to provide an improved frequency adjustingapparatus having a large adjustment range, and causing no increase inthe equivalent resistance.

Another object of the present invention is to provide a frequencyadjusting apparatus of the above-described type which is capable ofeffecting a continuous operation using equipment which does not requirea high vacuum.

In accomplishing these and other objects, a frequency fine-adjustingapparatus according to the present invention includes a laser beamgenerator for emitting a laser beam having a wavelength of 2 μm or less,a target material having a metallic layer, means for feeding the targetmaterial in the condition in which the metallic layer confronts a mainelectrode of a piezo-electric oscillator and is spaced a predeterminedlength from the main electrode, and an optical system for applying thelaser beam to the metallic layer.

When the laser beam is applied to the metallic layer, part of themetallic layer is vaporized and adheres to the surface of the mainelectrode, thereby finely adjusting the oscillation frequency of thepiezo-electric oscillator.

In another aspect of the present invention, a frequency fine-adjustingapparatus includes a laser beam generator for emitting a laser beamhaving a wavelength of 2 μm or less, a metal-containing target material,an optical system for applying the laser beam to the target material,and means for rotating the target material.

When the laser beam is applied to the target material, part of thetarget material is vaporized, is directed to a main electrode of thepiezo-electric oscillator by the rotating means and is adhered to thesurface of the main electrode.

In the apparatus according to the present invention, the target materialis accommodated in a sealed chamber, which is evacuated prior tofrequency fine-adjustment. However, the degree of the vacuum inside thesealed chamber is not relatively high.

As described above, according to the present invention, the laser beamis applied to the metal-containing material through a glass window ofthe sealed chamber so that vaporized material may adhere to the mainelectrode of the piezo-electric oscillator for the purpose of finelyadjusting the oscillation frequency of the oscillator.

Although the apparatus according to the present invention employs alaser beam generator for emitting the laser beam, the main electrode isnot removed by the laser beam, unlike in the conventional case. Thisfact contributes to less deterioration in the equivalent resistance.Furthermore, the range of adjustment is relatively wide, as comparedwith the conventional evaporation method, and the degree of the vacuumin the sealed chamber is not high, thus enabling a continuous operation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome apparent from the following description taken in conjunction withthe preferred embodiment thereof with reference to the accompanyingdrawings, throughout which like parts are designated by like referencenumerals, and wherein:

FIG. 1 is a block diagram of a frequency fine-adjusting apparatus for apiezo-electric oscillator according to a first embodiment of the presentinvention;

FIG. 2 is an enlarged view of a processing part in the apparatus of FIG.1;

FIG. 3 is a block diagram of a frequency fine-adjusting apparatus for apiezo-electric oscillator according to a second embodiment of thepresent invention;

FIG. 4 is a partially sectioned front view of a conventional crystaloscillator; and

FIG. 5 is a block diagram of a conventional frequency fine-adjustingapparatus for the crystal oscillator of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, there is shown in FIG. 1 a block diagramof a frequency fine-adjusting apparatus for a piezo-electric oscillatoraccording to a first embodiment of the present invention. The apparatusis provided with a sealed chamber 6 and two sets of a YAG laser beamgenerator 1 for emitting a laser beam 2, a reflection mirror 3 forreflecting the laser beam 2, and a converging lens 4 for converging thelaser beam 2. The sealed chamber 6 is evacuated prior to frequencyfine-adjustment so that the internal pressure thereof may be set to 10⁻²Torr. The sealed chamber 6 is provided with two glass windows 5 throughwhich pass the laser beams 2 emitted from the laser beam generators 1.The sealed chamber 6 accommodates two sets of a feed roll 9 for feedinga film 7 having a metallic layer, a take-up roll 10 for winding the film7, and a plurality of guide rolls 8 for guiding the film 7.

When the oscillation frequency of a piezo-electric oscillator 12 isfinely adjusted, the oscillator 12 is initially accommodated in thesealed chamber 6 so that the metallic layer of the film 7 may confront amain electrode of the oscillator 12 and may be spaced a predeterminedlength therefrom. A laser beam 2 having a wavelength of 1.06 μm is thenemitted from each laser beam generator 1. The laser beam 2 is reflectedby the reflection mirror 3 and converged by the converging lens 4. Muchof the laser beam 2 passes through the glass window 5 and is focused onthe film 7. Since the film 7 is continuously fed from the feed roll 9towards the take-up roll 10, metal vapor 11 vaporized from the metalliclayer of the film 7 continuously adheres to the piezo-electricoscillator 12.

The oscillation frequency of the piezo-electric oscillator 12 ismeasured by a counter 33 through an oscillating circuit 32 and inputtedinto a comparator 34, in which the oscillation frequency is comparedwith a predetermined frequency. When the former has reached the latter,two control devices 36 cause respective laser beam generators 1 to stopemitting the laser beams 2 so that the evaporation may be terminated.

In this embodiment, since opposite surfaces of the piezo-electricoscillator 12 are simultaneously subjected to the evaporation, awell-balanced fine adjustment can be achieved.

FIG. 2 particularly depicts the state of evaporation effected in theabove-described embodiment.

As shown in FIG. 2, the film 7 consists of a transparent organic film 13and a metallic layer 14 bonded to each other. The piezo-electricoscillator 12 is provided with an oscillating reed 15 and two mainelectrodes 16 securely mounted on opposite surfaces of the oscillatingreed 15. A secondary electrode 17 is formed on each main electrode 16 bythe evaporation when the frequency of the piezo-electric oscillator 12is finely adjusted. The YAG laser beam 2 passes through the glass window5 and is applied to the film 7. The organic film 13 permits much of theYAG laser beam 2 to be transmitted therethrough so that the metalliclayer 14 is raised in temperature, melted and vaporized. For example,when a laser beam having a pulse width of 200 ns and a pulse energy of0.4 mJ is applied as the YAG laser beam 2, the secondary electrode 17 isformed by vaporized metallic particles each having a diameter ofapproximately 2 μm.

FIG. 3 depicts a frequency fine-adjusting apparatus for thepiezo-electric oscillator according to a second embodiment of thepresent invention.

As shown in FIG. 3, a sealed chamber 6 accommodates a metal-containingtarget material 18, and a mechanism 19 for rotating the target material18.

A laser beam 2 having a wavelength of 1.06 μm emitted from a laser beamgenerator 1 is directed to a converging lens 4 by a reflection mirror 3.A glass window 5 transmits therethrough much of the laser beam 2, whichis then focused on the target material 18. The target material on whichthe laser beam 2 is applied is raised in temperature, melted andvaporized. As a result, vaporized metal 11 is caused to adhere to a mainelectrode of a piezo-electric oscillator 12. In this embodiment, thelaser beam 2 is applied to the target material 18 while the targetmaterial 18 is being rotated by the mechanism 19. Accordingly, theamount of vaporized metal 11 and the direction thereof can be desirablycontrolled.

It is to be noted that the oscillation frequency can be measured usingthe same system as in the first embodiment.

As is clear from the foregoing description, according to the presentinvention, the oscillation frequency of a piezo-electric oscillator canbe finely adjusted by applying a laser beam to a target material fromthe outside of relatively low-vacuum equipment so that vaporizedmaterial may adhere to the surface of a main electrode. The apparatusaccording to the present invention can extend the range of adjustmentand makes it possible to perform the continuous operation without anydeterioration in the equivalent resistance.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to be notedhere that various changes and modifications will be apparent to thoseskilled in the art. Therefore, unless such changes and modificationsotherwise depart from the spirit and scope of the present invention,they should be construed as being included therein.

What is claimed is:
 1. A frequency fine-adjusting apparatus for apiezo-electric oscillator having at least one main electrode, saidapparatus comprising:at least one laser beam generator for emitting alaser beam having a wavelength of 2 μm or less; at least one targetmaterial having a metallic layer; a target material feed means forfeeding said target material relative to the piezo-electric oscillatorin a condition in which said metallic layer confronts the main electrodeof the piezo-electric oscillator and is spaced a predetermined lengthfrom the main electrode; and at least one optical system for applyingsaid laser beam to said metallic layer; whereby, when said laser beam isapplied to said metallic layer, part of said metallic layer is vaporizedand adheres to a surface of the main electrode, thereby finely adjustingan oscillation frequency of the piezo-electric oscillator.
 2. Theapparatus according to claim 1 further comprising a sealed chamber foraccommodating said target material and said target material feed means,wherein said sealed chamber is evacuated prior to frequencyfine-adjustment.
 3. The apparatus according to claim 1, wherein saidtarget material includes a transparent film.
 4. The apparatus accordingto claim 1, wherein said target material feed means comprises a feedroller and a take-up roller.
 5. The apparatus according to claim 1,wherein the piezo-electric oscillator is provided with two mainelectrodes on opposite sides thereof and the apparatus includes two setsof said laser beam generator, said target material, said target materialfeed means, and said optical system so that vaporized material adheresto both said main electrodes.
 6. A frequency fine-adjusting apparatusfor a piezo-electric oscillator, comprising:a laser beam generator foremitting a laser beam having a wavelength of 2 μm or less; ametal-containing target material; an optical system for applying saidlaser beam to said target material; and means for rotating said targetmaterial whereby, when said laser beam is applied to said targetmaterial, part of said target material is vaporized and directed to amain electrode of the piezo-electric oscillator by said rotating meansand adheres to a surface of the main electrode, thereby finely adjustingan oscillation frequency of the piezo-electric oscillator.